1. Field of the Invention
The present invention relates generally to a circuit breaker, and particularly concerns to a circuit breaker capable of smooth automatic resetting action.
2. Description of the Prior Art
A typical conventional circuit breaker is shown in FIG. 1 through FIG. 3 which are sectional side views of the circuit breaker. Therein FIG. 1 shows an OFF state, FIG. 2 shows an ON state and FIG. 3 shows a tripping state which is a state immediately after a tripping and before restoration. In these drawings, numeral 1 designates a case made of an insulating plastic resin mold, numeral 2 designates a handle which is cradably fulcrumed by a pin 101. A torsion spring 3 is wound around the pin 101 and one end of the torsion spring 3 is held by a part of the case and the other end thereof is held on a part of the handle 2 thereby to energize the handle 2 in anticlockwise direction. A U-shaped link 4 is rotatably held by its one end in a hole 202 of an internal lever 201 of the handle 2 and a roller 9 is rotatably held on the other end of the U-shaped link 4. A moving contact arm 5 having a moving contact 12 at its lower end is fulcrumed by a pin 6 which is fixed to the case 1 and has a roller-receiving-indent 5a, 5b at its top part. An engaging lever 7 having an engaging part 7a at its upper end and a pushing seat 7b at its upper side part is fulcrumed also by the pin 6, and the engaging lever 7 is energized by a torsion spring 8 in anticlockwise direction. Thereby, the engaging part 7a catches the roller 9 in the states other than an instant immediately after a tripping. A pin 11 fixed on the moving contact arm is pulled by a tension spring 14 which is fixed by its other end to a pin 13 mounted on the case 1. A fixed contact 15 is fixed on a part of the case 1, in a manner to face the moving contact 12 so as to touch the latter when the moving contact arm 5 is rotated anticlockwise by a clockwise rotation of the handle 2 and the leftward motion of the roller 9 due to a toggle motion of a toggle link system consisting of the internal lever 201 and the U-shaped link 4. A solenoid coil 17 being wound around a bobbin 25 and having a plunger 23 therein is connected between a terminal 19 and the fixed contact 15. The terminal 19 is for connecting to outside conductor (not shown) by a wire pressing member 20 and a screw 21. A yoke of the solenoid coil 17 is mounted on the case 1. The plunger 23 has a restoring spring 24 energizing it to the right direction and also has a rod 26 which is for pushing the engaging lever 7 when a very large overcurrent, for instance, a shortcircuit current flows. A bimetal 30 which is connected by a soft conductor 29 to the moving contact 12 is connected and mounted on a fixed contact 31, to which an outer conductor (not shown) is to be connected by a wire pressing member 32 and a screw 33. Numeral 34 designates an adjusting screw for fine adjustment of angle of the bimetal 30. The middle part of the bimetal 30 is covered by an insulation sheath 35. A known arc runner 36 is connected by its one end to the fixed conductor 31 and its other end is mounted on the base part of the case 1. Numeral 38 designates a known side plate made of inorganic substance and disposed in parallel direction of running of arc on both sides of the arc runner. A known arc extinguish chamber 42 having plural grids 43 disposed with predetermined gaps between a pair of side plates 44 is provided next to the arc runner 36.
The operation of the conventional circuit breaker is as follows. In both states of the OFF state shown in FIG. 1 and the ON state shown in FIG. 2 of the circuit breaker, the roller 9 is held by the engaging part 7a of the engaging lever 7 and the roller-receiving-indent 5a, 5b of the moving contact arm 5, and thereby the U-shaped link 4 is fixed in the positions shown in FIG. 1 and FIG. 2, respectively.
When the handle 2 is rotated from the OFF state of FIG. 1 to ON state of FIG. 2, the toggle link system constituted by the internal lever 201 and the U-shaped link 4 moves upwards passing a dead point to the state of FIG. 2 and the toggle link system is extended thereby.
Accordingly the moving contact arm 5 is rotated anticlockwise around the pin 6, thereby making the moving contact 12 touch the fixed contact 16 as shown in FIG. 2.
On the contrary, when the handle 2 is rotated anticlockwise to the OFF state of FIG. 1, the toggle link system moves downwards to the original bent-shaped relation shown in FIG. 1, thereby rotating the moving contact arm 5 in clockwise direction around the pin 6, and the moving contact 12 is detached from the fixed contact 16 as shown in FIG. 1.
When a relatively moderate overcurrent, for instance, an overload current arises, the bimetal 30 is heated by its Joule heat due to the overcurrent flowing therethrough and is bent towards the moving contact arm 5, and hence the pushing seat 7b is pushed clockwise. Accordingly, by the right hand displacement of the engaging part 7a, the engagement of the roller 9 in the roller-receiving-indent 5a, 5b is released. Therefore, the moving contact arm 5 is rotated clockwise by the force of the tension spring 14, and the moving contact 12 is detached from the fixed contact 16, and a tripping state as shown in FIG. 3 is produced. Thereafter, by means of the torsion spring 3, the handle 2 is automatically rotated anticlockwise, and then the toggle link system restores to the state of FIG. 1 by falling of the roller 9 in a gap formed between the roller-receiving-indent 5a, 5b and the engaging part 7a. Thus, the state of the circuit breaker is restored to the OFF state shown in FIG. 1. In such moderate overcurrent case, the tripping and restoration of the circuit breaker proceed in an appropriate time delays induced by slow bending and restoring of the bimetal 30.
On the other hand, when a large overcurrent, for instance, by a shortcircuit current arises, the coil 17 is excited by the large current and the plunger 23 is driven leftwards in a high speed motion overcoming the force of the restoring spring 24, and hence the rod 26 strongly pushes the engaging lever 7 leftwards thereby driving it clockwise. As a result, the engaging part 7a releases the holding of the roller 9 and therefore the toggle link system constituted by the internal lever 201 and the U-shaped link 4 is released from the roller-receiving-indent 5a, 5b of the moving contact arm 5. And thereby, the moving contact arm 5 is rotated clockwise by means of the tension spring 14. Accordingly the moving contact 12 detaches from the fixed contact 16, thereby making a disconnection, and a tripping state as shown in FIG. 3 is produced. Thereafter, by meahs of the torsion spring 3, the handle 2 is automatically rotated anticlockwise, and then the toggle link system restores to the state of FIG. 1 by falling of the roller 9 in a gap formed between the roller-receiving-indent 5a, 5b and the engaging part 7a. Thus, the state of the circuit breaker is restored to the OFF state shown in FIG. 1. This large overcurrent tripping proceeds in a high speed motion.
The problem of the above-mentioned conventional circuit breaker is that, in a resetting action which after the tripping, since the motion of the roller 9 is rather free around the engaging part 7a, sometimes the roller 9 undesirably rides over wrong side of the engaging part 7a and caught by the engaging part 7a at the wrong side. Therefore, reliability of automatic resetting of the toggle link system is not sufficiently high.